Hiya:
SSRI's are notorious for causing difficulty in erections; in getting them, in maintaining them, and (I'v eheard form a dear friend) once you get it and maintain in, finding completion can become a problem. As he put it: he went on and on and on, and no result.
My husband also takes SSRI's... we found that, while the effect lasted quite a while, once his doctor lowered the SSRI and balanced it our with Wellbutrin, he seemed to level out. It sounds like you are a bit younger than he (he will be 50 this year), and maybe those enhancers are another option...I suggest that, regardless, you speak to your girlfirend if this is a long-term trusting relationship. Especially if you have ever had trouble finishing. Take it from a woman: if you have a problem, her first thought may be that it is because of her. That is a devastating thought.
I wish you luck...don't be embarrassed to talk to your doctor. It's more important to have your doctor aware of ALL of your health than to maybe miss an important symptom.